Molybdenum compounds are well-known for improving the properties of lubrication oils for internal combustion engines. Lubricating oils containing soluble molybdenum are known for reducing friction between moving parts in internal combustion engines, thereby improving fuel economy and increasing engine life through reduced wear.
A number of methods for preparing molybdenum-containing alkaline earth metal sulfonates have been disclosed in the art.
U.S. Pat. No. 3,496,105 (LeSuer) teaches a process for preparing molybdenum-containing alkaline earth metal sulfonates wherein an overbased carbonate alkaline earth metal sulfonate is contacted with an inorganic composition including ammonium and alkaline earth metal salts of a molybdenum-containing anion such as MoO.sub.4 and Mo.sub.7 O.sub.24. This process is characterized by the presence of a special peptizing agent required for the molybdenum-containing compound. These products, which are prepared directly from overbased carbonate materials, also suffer the disadvantage that the molybdenum incorporated in the composition can form a solid precipitate or a hazy precipitate, rendering the molybdenum-containing sulfonate material useless for lubricating oils. While haze in the lubricating oil composition does not always reduce the lubricant properties, solid precipitate can cause plugging of channels in engines and mechanical damage.
In U.S. Pat. No. 4,601,837, Valcho discloses a process for preparing overbased molybdenum alkaline earth metal sulfonate dispersions wherein a mixture is prepared from a sulfonic acid partially neutralized with ammonia, an alkaline earth metal compound, an alkanol of from one to seven carbon atoms and water. This mixture is hydrated by application of heat to produce an alkaline earth metal compound to which is added a molybdenum-containing compound and then an acidic material to form a molybdenum alkaline earth metal overbased sulfonate. Such a method of adding a molybdenum-containing compound before the addition of an acidic material has been termed a "mid-method of addition" of adding a molybdenum-containing compound to the hydrated alkaline earth metal compound. The "mid-method", as described above, suffers from the problem that the molybdenum-containing compound must be added to the hydrated alkaline earth metal compound before addition of the acidic material, thus requiring addition of the molybdenum compound during the process of preparing the molybdenum-alkaline earth metal sulfonate.
Accordingly, a need exists to provide a process for preparation of molybdenum-alkaline earth metal or alkali metal sulfonates that does not require the use of peptizing agents, that does not require the use of succinic anhydride to reduce haze, and which can be applied equally to sulfonates or phenates or salicylates, which sulfonates are not hazy, do not contain solid precipitate that can cause plugging of channels in engines and mechanical damage, and which provide anti-wear, anti-rust and anti-oxidation properties to lubricating oils and can be prepared from "off-the-shelf" alkaline earth metal or alkali metal sulfonates, phenates or salicylates.
There has now been found and developed an improved and flexible process, a so-called "post method," for producing highly basic molybdenum-alkaline earth metal and alkali metal overbased sulfonates, phenates and salicylates by an economical, efficient productive process resulting in substantial incorporation of the molybdenum into the sulfonate, phenate or salicylate which, when added to a lubricating oil, provides substantial anti-rust, anti-oxidation, and anti-wear properties to the oil and reduces the coefficient of friction of the oil. Such a method of adding a molybdenum-containing compound to an already-prepared sulfonate, phenate or salicylate compound or dispersion is termed a "post method" of addition.
The sulfonates, phenates or salicylates can be overbased calcium, barium, sodium, magnesium, strontium, potassium, or rubidium compounds. The phenates and salicylates can be sulfurized alkyl compounds. The phenates can be calcium or magnesium Mannich phenates.
The general object of this invention is to improve the properties of lubricating oils with an oil-soluble molybdenum compound wherein the molybdenum compound is incorporated into the lubricating oil in a convenient, economical method. The incorporation of molybdenum into alkaline earth of alkali metal sulfonates, phenates or salicylates is often accomplished in a convenient method if the molybdenum is in the form of a soluble compound in an aqueous solution as in U.S. Pat. No. 3,541,014 which teaches an aqueous solution of molybdate or paramolybdate. Other methods of incorporating molybdenum can require the presence of water. For example, U.S. Pat. No. 4,474,673 teaches addition of water to the reaction product of molybdenum halide and sulfurized organic compound to remove excess halide. U.S. Pat. No. 4,478,729 indicates the reaction product of a molybdenum halide with a sulfonic acid compound is preferably hydrolyzed with water. However, addition of water in preparation of overbased calcium sulfonates can result in a viscous opaque product which is unsuitable for use in a lubricating oil composition (Paper No. 10, International Corrosion Forum, Corrosion/75, National Assn. of Corrosion Engineers, Apr. 14-18, 1975, Toronto, Canada).
The present invention provides a convenient, economical method for incorporating molybdenum into an overbased alkaline earth or alkali metal sulfonate wherein the resulting product is clear, haze-free, precipitate-free and is suitable for use in a lubricating oil compositions despite the use of water as a solubilizing agent.